DE. J. P. JOULE ON THE SUEEACE - CONDENSATION OE STEAM. 
139 
The results of my experiments were quite in conformity with Professor Thomson’s 
view as to the smallness of the resistance to conduction through the thickness of the 
metal compared with the resistance at the surfaces of the tubes through the closely 
adhering film of fluid. I therefore sought to discover in each instance the entire con- 
ductivity by the formula 
where, a being the area of the tube in square feet, and w the quantity of refrigerating 
water transmitted per hour, C represents the number of units of heat, in lbs. of water 
raised 1°, which would be conducted through a surface of 1 foot area, the opposite sides 
of which difier from one another by 1°. The determinations of C in each instance will 
be found in column 18. 
I generally obtained observations of the vacuum-gauge directly after the stoppage of 
the condensation. The results of these, reduced to the value they would have had at 
the precise time of the closing of the stopcock, are given in column 15 of the Table. 
The effect of stopping the condensation was generally a diminution of pressure, which 
took place rapidly at first, and afterwards slowly and with great regularity. I believe 
that this diminution of pressure is owing to the water collected in the receiver, which, 
ha'ving fallen somewhat in temperatm’e during an experiment, governs the vacuum as 
soon as the fresh hot condensed water ceases to be supplied to its surface. In some 
few instances the mercui-y in the gauge was observed to fall immediately on the stoppage 
of the condensation. In these the vacuum appeared to be more perfect while the con- 
densation was being carried on than was due to the temperature of the condensed water. 
It was long before I was able to form any conjecture as to the cause of this anomalous 
circumstance. I now think that it might have been occasioned by a stricture in the 
india-rubber junction which connected the gauge with the steam-tube It is not, 
however, easy to see how this can account for the sudden fall of the gauge at the 
moment of the stoppage of the condensation. In the Table, I have marked those 
results which I suspect to have been influenced by a contraction at the junction, by a 
note of interrogation. I may observe that the india-rubber tubulures were frequently 
renewed, in order to prevent the chance of a stricture, which, moreover, I always 
endeavoured to detect at its first approach, by observing whether the mercury descended 
instantaneously on the admission of tlie first bubble of air into the receiver when the 
nut was unscrewed. 
Great care was always taken to keep the flow of steam and refrigerating water as con- 
stant as possible during each experiment. If this had not been done, the temperature 
of the water collected in the receiver during the former part of an experiment would 
have influenced to a certain extent the vacuum observed at the latter part. It was easy, 
by first condensing rapidly, and afterwards slowly by partially closing the steam-cock, 
to maintain for some time a vacuum much more perfect than that due to the tempera- 
tm’e of the water in the receiver. In this case “bumping boiling” took place in the 
receiver, whilst the pressure gradually decreased to the value due to the new conditions. 
